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Electronic Ignition System Description

The electronic ignition system produces and controls the high energy secondary spark. This spark ignites the compressed air/fuel mixture at precisely the correct time, providing optimal performance, fuel economy, and control of exhaust emissions. The engine control module (ECM) collects information from the crankshaft position sensor and the camshaft position sensor - inlet and camshaft position sensor - exhaust to determine the sequence, dwell, and timing of the spark for each cylinder. The ECM transmits a frequency signal to the ignition coil assembly on the appropriate ignition control circuit to fire the spark plugs.

The crankshaft position sensor circuits consist of an engine control module (ECM) supplied 5 V reference circuit, low reference circuit, and an output signal circuit. The crankshaft position sensor is an externally magnetically biased digital output integrated circuit sensing device. The sensor provides a pulse for each magnetic pole of the magnetic encoder wheel on the crankshaft. Each pole on the encoder wheel is spaced at 58-pole spacing, with 2 missing poles for the reference gap. The crankshaft position sensor produces an ON/OFF DC voltage of varying frequency, with 58 output pulses per crankshaft revolution. The frequency of the crankshaft position sensor output depends on the velocity of the crankshaft. The crankshaft position sensor sends a digital signal, which represents an image of the crankshaft encoder wheel, to the ECM as each pole on the wheel rotates past the crankshaft position sensor. The ECM uses each crankshaft position sensor signal pulse to determine crankshaft speed and decodes the crankshaft encoder wheel reference gap to identify crankshaft position. This information is then used to determine the optimal ignition and injection points of the engine. The ECM also uses crankshaft position sensor output information to determine the camshaft position sensor - inlet and camshaft position sensor - exhaust relative to the crankshaft, to control camshaft phasing, and to detect cylinder misfire.

The crankshaft encoder wheel is part of the crankshaft. The encoder wheel consists of 58 poles and a reference gap. Each pole on the encoder wheel is spaced 6° apart with a 12° space for the reference gap. The pulse from the reference gap is known as the sync pulse. The sync pulse is used to synchronise the coil firing sequence with the crankshaft position, while the other poles provide cylinder location during a revolution.

The camshaft position sensor - inlet and camshaft position sensor - exhaust is triggered by a notched reluctor wheel built onto the inlet camshaft sprocket. The camshaft position sensor - inlet and camshaft position sensor - exhaust provides four signal pulses to every camshaft revolution. Each notch, or feature of the reluctor wheel is of a different size which is used to identify the compression stroke of each cylinder and to enable sequential fuel injection. The camshaft position sensor - inlet and camshaft position sensor - exhaust is connected to the ECM by the following circuits:

The ignition coil assembly used on this engine integrates the 4 coils and the module within a single sealed component.

The ignition coil has the following circuits:

The ECM controls the individual coils by transmitting timing pulses on the ignition control circuit of each ignition coil to enable a spark event.

The spark plugs are connected to each coil by a short boot. The boot contains a spring that conducts the spark energy from the coil to the spark plug. The spark plug electrode is coated with platinum for long wear and higher efficiency.

The ECM controls all ignition system functions, and constantly adjusts the spark timing. The ECM monitors information from various sensor inputs that include the following: